Disable Hardware Checksum Offload for USB Ethernet Adapter

Currently I work on a patch for pfSense 2.3 alpha concerning DHCPv6 https://redmine.pfsense.org/issues/4206.
So to test out the patch and to make my day a little easier I bought a USB Ethernet dongle that uses a AX88772B. It works fine, but it turns out to get it to work under pfSense (running FreeBSD 10.2) you’ll need to switch off checksum offloading for TX and RX. You can do that with a call to:
ifconfig devicename -txcsum -rxcsum
, but it is more pratical to ask pfSense to do that at boot by going to ‘System / Advanced / Networking’ and tick ‘Disable hardware checksum offload’ (found in ‘Network Interfaces’ subsection under ‘Hardware Checksum Offloading’)
Update: I forgot to mention that disabling hardware checksum offload was needed, because pfSense ran in a virtual environment.